The invention relates to pigments containing carbon black and having improved abrasion resistance and to a process for their preparation.
It is known to achieve special color effects by incorporation of carbon black in pigments. However, the known processes have in some cases substantial disadvantages.
German Auslegeschrift 1,165,182 describes a complicated process by which the carbon black is formed by pyrolysis of organic compounds in the presence of the pigments to be coated. In this process, the carbon black is naturally precipitated in the presence of organic compounds only on the pigment surface. This smooths out the spaces between TiO.sub.2 particles applied to a microsurface.
Some disadvantages of this complicated pyrolysis process are eliminated in German Patent 2,557,796. In the process described there, first a substrate dispersion is mixed with a carbon black dispersion. The addition of a metal salt solution under hydrolysis conditions results in precipitation of a metal hydroxide film containing carbon black on the substrate. The products prepared in this manner are separated off and dried at 110.degree.-130.degree. C. However, it has been found that the dried pigments are unsuitable for various areas of application, since their wear resistance is insufficient. This property is extremely desirable especially for incorporation in cosmetics.
In the processes disclosed in the prior art, precipitation of the carbon black is not quantitative, i.e., some of the carbon black is present on the pigment in agglomerated form, so that the pigments do not have good hiding power. The unprecipitated carbon black has to be removed by sedimentation, which is time-consuming and cost-intensive.
A further disadvantage is the often observable bleeding of the carbon black upon suspension of the pigments in organic solvents for preparing coating systems.